/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_ipsec.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/callout.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/syslog.h>
#include <sys/protosw.h>
#include <sys/random.h>

#include <vm/uma.h>

#include <net/route.h>
#include <net/if.h>
#include <net/if_var.h>
#include <net/vnet.h>

#include <netinet/in.h>
#include <netinet/in_kdtrace.h>
#include <netinet/in_pcb.h>
#include <netinet/in_systm.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netinet/ip_var.h>
#ifdef INET6
#include <netinet/ip6.h>
#include <netinet6/in6_pcb.h>
#include <netinet6/ip6_var.h>
#include <netinet6/scope6_var.h>
#include <netinet6/nd6.h>
#endif
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_log_buf.h>
#include <netinet/tcpip.h>

#include <netinet/udp.h>
#include <netinet/udp_var.h>

#include <netipsec/ipsec_support.h>

#include <machine/in_cksum.h>

#include <security/mac/mac_framework.h>

static u_int
tcp_eff_msl(struct tcpcb *tp)
{
        struct inpcb *inp = tptoinpcb(tp);
#ifdef INET6
        bool isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
#endif

        if (
#ifdef INET6
            isipv6 ? in6_localip(&inp->in6p_faddr) :
#endif
#ifdef INET
            in_localip(inp->inp_faddr))
#else
            false)
#endif
                return (V_tcp_msl_local);
        else
                return (V_tcp_msl);
}

/*
 * Move a TCP connection into TIME_WAIT state.
 *    inp is locked, and is unlocked before returning.
 *
 * This function used to free tcpcb and allocate a compressed TCP time-wait
 * structure tcptw.  This served well for 20 years but is no longer relevant
 * on modern machines in the modern internet.  However, the function remains
 * so that TCP stacks require less modification and we don't burn the bridge
 * to go back to using compressed time-wait.
 */
void
tcp_twstart(struct tcpcb *tp)
{
        struct inpcb *inp = tptoinpcb(tp);

        NET_EPOCH_ASSERT();
        INP_WLOCK_ASSERT(inp);

        /* A dropped inp should never transition to TIME_WAIT state. */
        KASSERT((inp->inp_flags & INP_DROPPED) == 0, ("tcp_twstart: "
            "(inp->inp_flags & INP_DROPPED) != 0"));

        tcp_state_change(tp, TCPS_TIME_WAIT);
        tcp_free_sackholes(tp);
        soisdisconnected(inp->inp_socket);

        if (tp->t_flags & TF_ACKNOW)
                (void) tcp_output(tp);

        tcp_timer_activate(tp, TT_2MSL, 2 * tcp_eff_msl(tp));
        INP_WUNLOCK(inp);
}

/*
 * Returns true if the TIME_WAIT state was killed and we should start over,
 * looking for a pcb in the listen state.  Otherwise returns false and frees
 * the mbuf.
 *
 * For pure SYN-segments the PCB shall be read-locked and the tcpopt pointer
 * may be NULL.  For the rest write-lock and valid tcpopt.
 */
bool
tcp_twcheck(struct inpcb *inp, struct tcpopt *to, struct tcphdr *th,
    struct mbuf *m, int tlen)
{
        struct tcpcb *tp = intotcpcb(inp);
        char *s;
        int thflags;
        tcp_seq seq;

        NET_EPOCH_ASSERT();
        INP_LOCK_ASSERT(inp);

        thflags = tcp_get_flags(th);
#ifdef INVARIANTS
        if ((thflags & (TH_SYN | TH_ACK)) == TH_SYN)
                INP_RLOCK_ASSERT(inp);
        else {
                INP_WLOCK_ASSERT(inp);
                KASSERT(to != NULL,
                    ("%s: called without options on a non-SYN segment",
                    __func__));
        }
#endif

        /*
         * NOTE: for FIN_WAIT_2 (to be added later),
         * must validate sequence number before accepting RST
         */

        /*
         * If the segment contains RST:
         *      Drop the segment - see Stevens, vol. 2, p. 964 and
         *      RFC 1337.
         */
        if (thflags & TH_RST)
                goto drop;

#if 0
/* PAWS not needed at the moment */
        /*
         * RFC 1323 PAWS: If we have a timestamp reply on this segment
         * and it's less than ts_recent, drop it.
         */
        if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
            TSTMP_LT(to.to_tsval, tp->ts_recent)) {
                if ((thflags & TH_ACK) == 0)
                        goto drop;
                goto ack;
        }
        /*
         * ts_recent is never updated because we never accept new segments.
         */
#endif

        /* Honor the drop_synfin sysctl variable. */
        if ((thflags & TH_SYN) && (thflags & TH_FIN) && V_drop_synfin) {
                if ((s = tcp_log_addrs(&inp->inp_inc, th, NULL, NULL))) {
                        log(LOG_DEBUG, "%s; %s: "
                            "SYN|FIN segment ignored (based on "
                            "sysctl setting)\n", s, __func__);
                        free(s, M_TCPLOG);
                }
                goto drop;
        }

        /*
         * If a new connection request is received
         * while in TIME_WAIT, drop the old connection
         * and start over if the sequence numbers
         * are above the previous ones.
         * Allow UDP port number changes in this case.
         */
        if (((thflags & (TH_SYN | TH_ACK)) == TH_SYN) &&
            SEQ_GT(th->th_seq, tp->rcv_nxt)) {
                /*
                 * In case we can't upgrade our lock just pretend we have
                 * lost this packet.
                 */
                if (INP_TRY_UPGRADE(inp) == 0)
                        goto drop;
                if ((tp = tcp_close(tp)) != NULL)
                        INP_WUNLOCK(inp);
                TCPSTAT_INC(tcps_tw_recycles);
                return (true);
        }

        /*
         * Send RST if UDP port numbers don't match
         */
        if (tp->t_port != m->m_pkthdr.tcp_tun_port) {
                if (tcp_get_flags(th) & TH_ACK) {
                        tcp_respond(tp, mtod(m, void *), th, m,
                            (tcp_seq)0, th->th_ack, TH_RST);
                } else {
                        if (tcp_get_flags(th) & TH_SYN)
                                tlen++;
                        if (tcp_get_flags(th) & TH_FIN)
                                tlen++;
                        tcp_respond(tp, mtod(m, void *), th, m,
                            th->th_seq+tlen, (tcp_seq)0, TH_RST|TH_ACK);
                }
                INP_UNLOCK(inp);
                TCPSTAT_INC(tcps_tw_resets);
                return (false);
        }

        /*
         * Drop the segment if it does not contain an ACK.
         */
        if ((thflags & TH_ACK) == 0)
                goto drop;

        INP_WLOCK_ASSERT(inp);

        /*
         * If timestamps were negotiated during SYN/ACK and a
         * segment without a timestamp is received, silently drop
         * the segment, unless the missing timestamps are tolerated.
         * See section 3.2 of RFC 7323.
         */
        if (((to->to_flags & TOF_TS) == 0) && (tp->ts_recent != 0) &&
            (V_tcp_tolerate_missing_ts == 0)) {
                goto drop;
        }

        /*
         * Reset the 2MSL timer if this is a duplicate FIN.
         */
        if (thflags & TH_FIN) {
                seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
                if (seq + 1 == tp->rcv_nxt)
                        tcp_timer_activate(tp, TT_2MSL, 2 * tcp_eff_msl(tp));
        }

        /*
         * Acknowledge the segment if it has data or is not a duplicate ACK.
         */
        if ((thflags & (TH_SYN | TH_FIN)) != 0 || tlen != 0 ||
            th->th_seq != tp->rcv_nxt || th->th_ack != tp->snd_nxt) {
                TCP_LOG_EVENT(tp, th, NULL, NULL, TCP_LOG_IN, 0, tlen, NULL,
                    true);
                TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
                tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
                    tp->snd_nxt, TH_ACK);
                INP_UNLOCK(inp);
                TCPSTAT_INC(tcps_tw_responds);
                return (false);
        }
drop:
        TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
        INP_UNLOCK(inp);
        m_freem(m);
        return (false);
}